Knoop Diamond Research Articles

Is the whitening effect of charcoal-based dentifrices related to their abrasive potential or the ability of charcoal to adsorb dyes?

ObjectivesTo evaluate if tooth color alteration of activated charcoal-based dentifrices may be attributed to the dye adsorption potential of charcoal (chemical action - C - slurry only) or to the association of dye adsorption with abrasion (chemo-mechanical action - CM- slurry/toothbrushing). Potential adverse effects in surface roughness, gloss, and wear were also assessed. MethodsBovine enamel/dentin specimens were randomly allocated into the groups according to treatments and test model (n = 15): deionized water (negative control- NC); Colgate Maximum Anticaries Protection (conventional toothpaste- positive control- PC); Colgate Luminous White Activated Charcoal (LW); Oral-B 3D White Therapy Charcoal (WT); Curaprox Black is White (BW); Dermavita Whitemax (Activated charcoal powder- WP). Specimens were exposed to the C or CM models, in 28-day staining-treatment cycling. Color change (ΔE00), whiteness index (ΔWID), percentage of alteration of surface roughness (%Raalt), and gloss (%GUalt) were calculated. Additional specimens (n = 9) were indented with a Knoop diamond and subjected to 100,000 abrasion cycles. Enamel wear was determined by calculating the decrease in indentations geometry. Data were analyzed by ANOVA/Tukey tests (α = 0.05). ResultsThe CM-model produced lower color change (staining) than C (p = 0.0001). PC, LW, WT, BW, and WP showed similar color results for both models, differing from NC (p < 0.05).%Ra and%GU did not differ among the C-model groups (p > 0.05) and WP exhibited the highest variation (%Ra and%GU) under CM-model. Enamel wear values were lowest in the NC and PC groups, intermediate for LW, WT, BW, and highest for the WP (p < 0.05). ConclusionActivated charcoal-based dentifrices have a similar ability to minimize tooth staining as the conventional toothpaste, with increased enamel wear potential in the long term (after 100,000 cycles). The activated charcoal powder damaged the enamel surface, showing a higher deleterious effect on enamel roughness, gloss, and wear. Clinical significanceDentifrices containing activated charcoal do not provide superior results to minimize tooth staining compared to conventional toothpaste. Charcoal powder should be used with caution because it promotes higher superficial alterations on the enamel surface.

Relationship between fracture toughness and fractal dimensional increment in two types of dental glass-ceramics with different fracture surface roughness.

Previous studies have reported the fractal dimensional increment of glass-ceramic fracture surfaces. The objective of this study was to determine the relationship between fracture toughness and fractal dimensional increment of two dental glass-ceramics with different volume fraction of crystals and different fracture surface roughness. Bar-shaped specimens were prepared from lithium disilicate (LDS) and nanofluorapatite (NFA) glass-ceramics. One face of each specimen was indented using a Knoop diamond at 25N (LDS) or 10N (NFA) followed by loading in 4-point, or 3-point flexure, respectively, until failure. Fracture toughness (Kc) was calculated using the surface crack in flexure (SCF) technique (ASTM C1421). Epoxy replicas of the fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine the fractal dimensional increment (D*) by the Minkowski cover algorithm. Median (25%, 75% quartiles) fracture toughness of LDS bars were 1.62 (1.59, 1.69)MPam1/2 and NFA bars were 0.68 (0.66, 0.74)MPam1/2, respectively. The median fractal dimension (D) value (25%, 75% quartiles) before noise filtering were 2.16 (2.15, 2.17) and after noise filtering were 2.14 (2.14, 2.15) for LDS and before noise filtering were 2.29 (2.21, 2.38) and after noise filtering were 2.17 (2.17, 2.18) for NFA. Median (25%, 75% quartiles) surface roughness (Ra) before noise filtering were 139 (119, 188)nm and after noise filtering were 137 (118, 187)nm for LDS and before noise filtering were 7 (6, 15)nm and after noise filtering were 7 (6, 15)nm for NFA. Noise filtering successfully eliminated noise from the material with smooth fracture surfaces (NFA), decreasing the measured fractal dimension. The NFA data fit a Kc vs. D*1/2 statistical model for fused silica previously tested using a similar technique. The equation relating fracture toughness to the fractal dimension was modified, accounting for the toughening mechanisms. Fractal analysis with noise filtering can be used to estimate the fracture toughness of dental glass-ceramics that do not exhibit crack bridging.

Effects of concentration of sodium hypochlorite as an endodontic irrigant on the mechanical and structural properties of root dentine: A laboratory study.

AimThe use of high‐concentration sodium hypochlorite (NaOCl) as an endodontic irrigant remains controversial because of its potential impact on the fracture strength of endodontically treated teeth. This study evaluated the effects of using different NaOCl concentrations, with 2‐min‐ethylenediaminetetraacetic acid (EDTA) as the final active irrigant, on the biomechanical and structural properties of root dentine.MethodologyA new test method, which is more clinically relevant, was utilized to calculate the fracture strength of root dentine. Bovine incisors were used to obtain root dentine discs. The root canals were enlarged to mean diameter of 2.90 mm with a taper of 0.06. The resulting discs were divided into five groups (n = 20) and treated with different concentrations of NaOCl (5.25%, 2.5%, and 1.3%) for 30 min plus 17% EDTA for 2 min. The discs were then loaded to fracture by a steel rod with the same taper through the central hole. The fractured specimens were examined by scanning electron microscopy to evaluate changes in the dimensions of the remaining intertubular dentine and the tubular radius. Micro‐hardness was also measured with a Knoop diamond indenter along a radius to determine the depth of dentine eroded by the irrigation. Results were analysed by one‐way anova and the Tukey test. The level of significance was set at α = 0.05.ResultsThe damage by NaOCl increased with its concentration. 5.25% NaOCl greatly reduced the fracture strength of root dentine from 172.10 ± 30.13 MPa to 114.58 ± 26.74 MPa. The corresponding reduction in micro‐hardness at the root canal wall was 34.1%. The damages reached a depth of up to 400 μm (p < .05). Structural changes involved the degradation of the intratubular wall leading to enlarged dentinal tubules and the loss of intertubular dentine. Changes in the microstructural parameters showed positive linear relationships with the fracture strength.ConclusionsWith the adjunctive use of EDTA, NaOCl caused destruction to the intratubular surface near the root canal and, consequently, reduced the root dentine's mechanical strength. The higher the concentration of NaOCl, the greater the effect. Therefore, endodontists should avoid using overly high concentration of NaOCl for irrigation to prevent potential root fracture in endodontically treated teeth.

M1 - Fracture Toughness and Fractal Dimension of Two Dental Glass-Ceramics

Studies have reported the fractal dimensional increment of glass and glass-ceramic fracture surfaces. The objective of this study was to determine the relationship between fracture toughness and fractal dimensional increment of two types of dental glass-ceramics with different volume fraction of crystals and different fracture surface roughness. Fifteen bar-shaped specimens were prepared from lithium disilicate (LDS) by sectioning the blocks (IPS e.max CAD, Ivoclar Vivadent). Ten beams were prepared by mixing and layering the nanofluorapatite (NFA) glass-ceramic powder (IPS e.max Ceram, Ivoclar Vivadent). One face of each of the specimens was indented using a Knoop diamond at 25 N (LDS) or 10 N (NFA) followed by loading in deionized water in 4-point, or 3-point flexure, respectively, until failure. Fracture surfaces were analyzed using scanning electron microscope (SEM). Fracture toughness (Kc) was calculated using the surface crack in flexure (SCF) technique (ASTM C1421). Epoxy replicas of the fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine the fractal dimensional increment (D*) by the Minkowski cover algorithm. In addition, surface roughness was computed from the AFM scans using the Gwyddion software. The median (25%, 75% quartiles) fracture toughness of LDS and NFA bars were 1.62 (1.59, 1.69) MPam1/2 and 0.68 (0.66, 0.74) MPam1/2, respectively. The median fractal dimension (D) value (25%, 75% quartiles) before and after noise filtering for LDS were 2.16 (2.15, 2.17) and 2.14 (2.14, 2.15), respectively, and for NFA were 2.29 (2.21, 2.38) and 2.17 (2.17, 2.18), respectively. The NFA follows the regression model (Y=1.99 X) between Kc and sqrt. D* for glasses as previous studies, but the LDS deviated from the model. The median (25%, 75% quartiles) surface roughness before and after noise filtering for LDS were 139 (119, 188) nm and 137 (118, 187) nm and for NFA were 7 (6, 15) nm and 7 (6, 15) nm, respectively. Noise filtering successfully eliminated noise from the AFM scans of the material with smooth fracture surfaces (NFA), resulting in a decrease in measured fractal dimension. The LDS data deviated from the model because of toughening due to crack bridging. Fractal analysis with noise filtering can be used to estimate the fracture toughness of dental glass-ceramics that do not exhibit crack bridging.

Ultimate tensile strength and microhardness of glass ionomer materials

Objective: This study evaluated the ultimate tensile strength (UTS) and microhardness (µKH) of conventional (CO) and hybrid resin-modified glass ionomer (RM). Material and methods: Nine specimens to UTS and twelve for µKHN of glass ionomer materials were obtained using special molds. The materials were manipulated and CO groups were allowed to self-cure for five minutes and RM were subjected to light-activation as indicated by manufactures through a glass slide. All specimens were dark-stored in 100% relative humidity for 24h. For UTS test, specimens were tested in tension in a universal testing machine (crosshead speed of 1 mm/min) until failure. For µKHN test a Knoop diamond indenter was used to make five indentations in the upper/light irradiated surface of the specimens. UTS and µKHN data were submitted to one-way ANOVA, followed by Tukey’s test (?= 5%). Results: The results for UTS were: Ionomaster: 7.0 (±1.6)A; Maxxion R: 8.8 (±3.7)A Vidrion R: 8.8 (±3.9)A; ChemFil Rock: 10.7 (±4.6)AB; Vitremer: 13.1 (±3.3)BC; Vitrofil R: 14.9 (±7.8)CD; Ionoseal: 14.5 (±8.2)CD; Resiglass: 16.3 (±2.3)D. The results for µKH: Ionomaster: 24.3 (±6.6)B; Maxxion R: 17.7 (±4.7)A, Vidrion R: 31.0 (±9.4) B; ChemFil Rock: 31.1 (±8.5)B; Vitremer: 20.3 (±3.3)A; Vitrofil R: 16.5 (±5.1)A; Ionoseal: 13.1 (±8.5)A; Resiglass: 21.6 (±5.2)A. Conclusion: It was observed that the hybrid resin-modified ionomers generally have higher cohesive strength than conventional ones, but lower microhardness.

Effect of Zinc Sulfate on Human Primary Enamel Microhardness: An in vitro Study

The aim of this study was to assess the effect of zinc sulfate on microhardness of human primary enamel. Sixteen sound primary molars were sectioned mesiodistally. For each sample one of the sections was randomly immersed in artificial saliva (Biotene, USA) and the other was immersed in artificial saliva which was charged with 10 mg/5 mL concentration of zinc sulfate supplement (Razak Company, Iran) daily. After 24 days (the expected time to use up one 120-mL bottle) the surface microhardness of enamel was measured by knoop hardness test (KH) with Knoop diamond under a 50-gram load for 10 seconds. The mean (+/- SD) microhardness values (KHV) for the tested groups were 320 +/- 49.45 and 357 +/- 36.35, respectively. There were statistically significant differences between the groups as exhibited by independent t-test (P = 0.023). Primary teeth immersed in a zinc sulfate rich solution for 24 days showed higher microhardness values in comparison with the control group.

The effect of toothpaste concentration on enamel and dentine wear in vitro

Objectives To determine the effect of toothpaste concentration on enamel and dentine wear in vitro and to model the effects of toothpaste abrasion upon dilution during toothbrushing in vivo. Methods Polished human enamel/dentine specimens were indented with a Knoop diamond and the enamel–dentine junction profiled. Specimens were brushed for 1200 s with toothpastes with differing relative dentine abrasivity (RDA), either Toothpaste A (RDA = 90) or Toothpaste B (RDA = 200), using a toothbrush mounted in a brushing machine. The toothpastes were dispersed in water and 1% sodium carboxymethyl cellulose to give a range of toothpaste concentrations. After brushing the Knoop indent length and the enamel–dentine step were remeasured and the wear to the enamel and dentine calculated. An equation for modelling the decrease in toothpaste concentration with brushing time was found using published in vivo data and used to estimate the level of dentine wear during in vivo brushing. Results The mean enamel wear was in the range 0.03–0.11 μm and there was only a small but non-significant ( p > 0.05) increase in enamel wear with toothpaste concentration. The mean dentine wear was in the range 0.28–27.63 μm and the dentine wear increased significantly ( p < 0.05) with toothpaste concentration, with Toothpaste B giving more wear than Toothpaste A. Analysis with published in vivo data showed that 50% of dentine wear occurs in the first 20 s of brushing and that the wear approaches a plateau value with brushing time as the toothpaste concentration is reduced. Conclusions Enamel wear increases only slightly with toothpaste concentration whereas dentine wear increases with toothpaste concentration.

Thickness of softened human enamel removed by toothbrush abrasion: an in vitro study

The aim of the study was to assess the thickness of softened enamel removed by toothbrushing. Human enamel specimens were indented with a Knoop diamond. Softening was performed with citric acid or orange juice. The specimens were brushed in a brushing machine with a manual soft toothbrush in toothpaste slurry or in artificial saliva. Enamel loss was calculated from the change in indentation depth of the same indent before and after abrasion. Mean surface losses (95% confidence interval) were recorded in treatment groups (in nanometers): (1) citric acid, abrasion with slurry = 339 (280-398); (2) citric acid, abrasion with artificial saliva = 16 (5-27); (3) orange juice, abrasion with slurry = 268 (233-303); (4) orange juice, abrasion with artificial saliva = 14 (5-23); (5) no softening, abrasion with slurry = 28 (10-46). The calculated thickness of the softened enamel varied between 254 and 323 nm, depending on the acid used.

Evaluation of superficial microhardness in dental enamel with different eruptive ages

This study evaluated the superficial microhardness of enamel in teeth at different posteruptive ages (before eruption in the oral cavity, 2-3 years after eruption, 4-10 years after eruption and more than 10 years after eruption). The study sample was composed of 134 specimens of human enamel. One fragment of each tooth was obtained from the flattest central portion of the crown to produce specimens with 3 x 3 mm. The enamel blocks were minimally flattened out and polished in order to obtain a flat surface parallel to the base, which is fundamental for microhardness testing. Microhardness was measured with a microhardness tester and a Knoop diamond indenter, under a static load of 25 g applied for 5 seconds. Comparison between the superficial microhardness obtained for the different groups was performed by analysis of Student's t test. The results demonstrated that superficial microhardness values have a tendency to increase over the years, with statistically significant difference only between unerupted enamel and that with more than 10 years after eruption. According to the present conditions and methodology, it was concluded that there were differences between the superficial micro-hardness of specimens at different eruptive ages, revealing an increasing mineralization. However, this difference was significant only between unerupted specimens and those with more than 10 years after eruption.

Controlled Toothbrush Abrasion of Softened Human Enamel

The aim of this in vitro study was to compare toothbrush abrasion of softened enamel after brushing with two (soft and hard) toothbrushes. One hundred and fifty-six human enamel specimens were indented with a Knoop diamond. Salivary pellicle was formed in vitro over a period of 3 h. Erosive lesions were produced by means of 1% citric acid. A force-measuring device allowed a controlled toothbrushing force of 1.5 N. The specimens were brushed either in toothpaste slurry or with toothpaste in artificial saliva for 15 s. Enamel loss was calculated from the change in indentation depth of the same indent before and after abrasion. Mean surface losses (95% CI) were recorded in ten treatment groups: (1) soft toothbrush only [28 (17–39) nm]; (2) hard toothbrush only [25 (16–34) nm]; (3) soft toothbrush in Sensodyne MultiCare slurry [46 (27–65) nm]; (4) hard toothbrush in Sensodyne MultiCare slurry [45 (24–66) nm]; (5) soft toothbrush in Colgate sensation white slurry [71 (55–87) nm]; (6) hard toothbrush in Colgate sensation white slurry [85 (60–110) nm]; (7) soft toothbrush with Sensodyne MultiCare [48 (39–57) nm]; (8) hard toothbrush with Sensodyne MultiCare [40 (29–51) nm]; (9) soft toothbrush with Colgate sensation white [51 (37–65) nm]; (10) hard toothbrush with Colgate sensation white [52 (36–68) nm]. Neither soft nor hard toothbrushes produced significantly different toothbrush abrasion of softened human enamel in this model (p > 0.05).

The protective nature of pellicle towards toothpaste abrasion on enamel and dentine

Objectives To determine the protective nature of pellicle towards toothpaste abrasion. Methods The enamel region of human enamel–dentine blocks was indented with a Knoop diamond and the profile across the enamel–dentine junction was measured. Blocks were either exposed to deionised water or placed onto intra-oral appliances and worn in the mouth to produce in situ pellicles. This was followed by a 10-day period of tooth brushing experiments. Each day, specimens were brushed with a slurry of either Toothpaste A (RDA = 90) or Toothpaste B (RDA = 204) for 25 cycles (10 s) on a brushing machine. This was repeated three times per day for a total of 750 brushing cycles. Between brushing cycles specimens were returned to water or in situ. The geometry of the Knoop indents and the enamel–dentine profile were re-measured and the enamel and dentine wear calculated. Specimens were also prepared for TEM analyses. Results The mean enamel wear (μm) for Toothpastes A and B (water) was 0.23 and 0.06, and for Toothpastes A and B ( in situ) was 0.03 and 0.08, respectively. The mean dentine wear (μm) for Toothpastes A and B (water) was 5.08 and 6.03, and for Toothpastes A and B ( in situ) was 1.94 and 1.70, respectively. For Toothpaste A, the presence of in situ pellicle significantly ( p < 0.05) reduced enamel and dentine wear compared to water and for Toothpaste B, dentine wear was significantly reduced compared to water. After tooth brushing, residues of the in situ pellicle layer could be detected on enamel and dentine surfaces by TEM analysis. Conclusions The study has demonstrated for the first time that the presence of pellicle can significantly reduce toothpaste abrasion.

The measurement of enamel wear by four toothpastes

To determine the enamel abrasivity of three whitening toothpastes and a silica toothpaste and to measure the brushing forces used. Polished human enamel blocks were indented with a Knoop diamond and attached to dentures of adult volunteers. The blocks were brushed ex vivo, twice per day with either a whitening toothpaste containing Perlite (White System), a commercial whitening toothpaste (A and B) or a silica toothpaste. After four and twelve-weeks, one block per subject was removed and the Knoop indent remeasured. From the changes in the indent length, the amount of enamel wear was calculated. The mean enamel wear (sd) for White System, silica toothpaste, whitening toothpaste A and B after four-weeks was 0.14 (0.15), 0.09 (0.16), 0.14 (0.12) and 0.89 (0.93) and after twelve-weeks was 0.24 (0.21), 0.37 (0.73), 0.36 (0.52) and 1.04 (0.98) microm respectively. After four-weeks, the differences in enamel wear between whitening toothpaste B and all other toothpastes were of statistical significance (p < 0.003), but not after twelve-weeks. The mean ex vivo normal brushing force (sd) was 2.67 (1.33) N. All three whitening toothpastes did not give significantly more enamel wear than a silica toothpaste after twelve-weeks in situ with ex vivo brushing.

Applicability of common methods for short time erosion analysis in vitro.

Dental erosion can be measured by different methods. The aim of the present study was to check the applicability of common methods to determine initial erosive effects. Enamel surfaces (4.5 mm2) were eroded in vitro by treatment with hydrochloric acid (pH 2, 2.3 and 2.6) for 5 to 60 s or 240 s, respectively. Erosive effects were assayed with three different methods: Knoop's diamond indentation, profilometry and the determination of the dissolved calcium ions (Ca2+) in a colorimetric assay based on the arsenazo-III-reaction. Erosive mineral loss of > 1 microm are measurable with profilometry. This corresponds to the erosive effects that occur after 60 s or more. Profilometric data yielded variance of up to 50%. Knoop's diamond indentation also showed some limitations: the depth of indentation reached a plateau after 30 to 120 s and the measurements showed variance of up to 85%. With the colorimetric assay, short time erosive effects occurring within 5 s could be assessed precisely and kinetically. The method allowed small amounts of 400 pmol Ca2+ per well to be quantified in small volumes with little variability. For evaluation and quantification of short time erosive effects, the colorimetric method is superior to diamond indentation and profilometry.

Influence of light polymerization modes on degree of conversion and crosslink density of dental composites

This study analyzed the influence of light polymerization modes on crosslink density (CD) and the degree of conversion (DC) of dental composites. A minifilled hybrid and a nanofilled dental composite were photoactivated with two light polymerization modes: Conventional-850 mW/cm2 for 20 s and Gradual-50 up to 1,000 mW/cm2 for 10 s+1,000 mW/cm2 for 10 s. DC was determined by the use of FT-Raman-spectrometer. A softening test, using Knoop diamond indentation, was carried out at the top and bottom of 2 mm thick dental composite disks, before and after storage in 100% ethanol for 24 h, in order to represent the amount of crosslink density. Data were analyzed by ANOVA and Student-Newman-Keuls' multiple range test (alpha=0.05). The DC was influenced by light polymerization modes, with Gradual mode presenting lower DC. On bottom surfaces, the nanofilled dental composite was more susceptible to softening by ethanol than minifilled hybrid, and gradual light polymerization of nanofilled dental composite resulted in more softening than when conventional light polymerization was used. The results suggest that nanofilled composites are capable undergoing more plasticization if applied in thick increments.

Susceptibility of Acid-Softened Enamel to Mechanical Wear – Ultrasonication versus Toothbrushing Abrasion

The study aimed to compare the amounts of softened enamel removable by ultrasonication and by toothbrushing abrasion of briefly eroded samples. Thirty bovine enamel samples were demineralized in hydrochloric acid (pH 2.1) for 60 s and were then either brushed with 350 brushing strokes in toothpaste slurry (group A) or distilled water (group B) or were ultrasonicated for 120 s (group C). Enamel loss was measured after 10, 20, 50 and then after every 50 brushing strokes or after 5, 30, 60 and 120 s ultrasonication. Samples were indented with a Knoop diamond after erosion, and enamel loss due to abrasion or wear was calculated from the change in indentation depth after mechanical treatment. Within- and between-group comparisons were performed by ANOVA or t test. Initially, enamel loss increased with increasing brushing treatment or ultrasonication time. Enamel loss did not increase after 300 brushing strokes in group A (534 ± 169 nm) or 250 brushing strokes in group B (423 ± 80 nm), or after 60 s ultrasonication (231 ± 72 nm). Enamel loss was significantly higher in groups A and B than in group C. The results confirm that ultrasonication removes only the outer, more highly demineralized part of the softened enamel layer. Results also indicate that toothbrushing abrasion removes more softened enamel from briefly eroded enamel than ultrasonication, and therefore probably removes partly demineralized enamel from the deeper part of the softened layer. In vivo, excessive toothbrushing might remove the softened enamel layer almost completely.

Association effect of in-office and nightguard vital bleaching on dental enamel microhardness

The aim of this study was to evaluate “in vitro” the microhardness of dental enamel subjected to in-office and nightguard vital bleaching agents: 37% carbamide peroxide-CP37 (Whiteness Super-FGM) and 10% carbamide peroxide-CP10 (Whiteness Perfect-FGM). Enamel fragments measuring 3 x 3mm (n=18) were embedded in polystyrene resin and polished. They were treated 1h once a week with the CP37 and 8h every day with CP10 for 21 days. The remainder of the time they were stored in remineralization solution. Microhardness measurements were completed with a Knoop diamond in a microhardness tester with 50g static load prior to the exposure to bleaching agents and 7, 14, 21, 28, and 35 days after that Split Plot ANOVA followed by Tukey’s test were performed. The test showed no significant differences in the enamel microhardness before, during, or after bleaching treatment. Conclusions: It can be concluded that the combination of in-office and nightguard vital bleaching agents do not alter the enamel microhardness “in vitro”.

A parametric study of implantation-induced variations on the mechanicalproperties of epitaxial GaN

Doping of GaN through ion implantation permits improved control of the dopantprofile and dose, while it also modifies the film’s mechanical properties suchas microhardness. We discuss the effect of Si+- and Mg+-ion implantationon the mechanical properties of GaN films grown by electron cyclotronresonance plasma-assisted molecular beam epitaxy on sapphire substrates.The changes of the mechanical properties are studied using the staticindentation method and they are discussed in conjunction with results fromnear-edge x-ray absorption fine-structure spectroscopy. Transmission electronmicroscopy is used for the microstructural characterization of selectedimplanted specimens. The static indentation test method was applied utilizingVickers and Knoop diamond indenters. The microhardness results areabsolved from the influence of the substrate through the implementation ofa well-established deconvolution method. The elastoplastic response ofthe films are compared and discussed on the basis of the proportionalspecimen resistance model and the form of the indentation size effect curves.

Ion implantation effects on the microhardness and microstructure of GaN

We study the effect of N + and O + implantation on the microhardness and the microstructure of epitaxially grown GaN. The microhardness is measured using a Knoop diamond indenter while information on the effect of implantation on the surface morphology, microstructure and electronic structure is provided by atomic force microscopy, cross-section transmission electron microscopy and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. It is demonstrated that implantation increases the surface microhardness. A possible mechanism for the surface hardening effect is based on the formation of N interstitials that pin the dislocations and prohibit the plastic deformation. In addition to the hardening effect, the implantation induced N interstitials introduce a characteristic resonance in the NEXAFS spectra, at 1.4 eV below the absorption edge.

Efeito cariostático de restaurações adesivas em superfícies radiculares: estudo in vitro

Materiais restauradores que liberam íons flúor e/ou promovem adesão à estrutura dental têm sido relacionados com a inibição do desenvolvimento de lesões de cárie adjacentes às restaurações. A hipótese testada neste estudo foi a de que o uso de resina composta/sistema adesivo tem efeito cariostático semelhante a um material adesivo que libera íons flúor - cimento de ionômero de vidro - sobre a superfície radicular adjacente às restaurações. Foram utilizadas 20 raízes de terceiros molares humanos extraídos, embutidas em resina de poliestireno e planificadas. Cavidades padronizadas foram preparadas e restauradas aleatoriamente com (a) Chelon-Fil (Espe) ou (b) Z100/SingleBond (3M). Valores iniciais (KHNi) de microdureza superficial Knoop da dentina foram obtidos a 100, 200 e 300 mim da margem oclusal das restaurações. Uma área de 2,0 mm ao redor da restauração foi delimitada e submetida à indução de cárie artificial. Obtiveram-se, então, os valores finais (KHNf) de microdureza, nas mesmas condições e localizações da leitura inicial. As diferenças entre KHNi e KHNf foram consideradas para a análise estatística. As medianas de KHNi - KHNf nas distâncias de 100, 200 e 300 mim foram para (a): -3,8; -0,3; -1,0; e para (b): 3,3; 2,5; 1,7. O teste de Kruskal-Wallis não evidenciou diferença significativa entre as distâncias dentro de cada grupo. Às distâncias de 200 e 300 mim, não houve diferença significativa entre os materiais avaliados. À distância de 100 mim, (a) diferiu significativamente de (b) (p &lt; 0,05). Sob as condições deste estudo, o cimento de ionômero de vidro apresentou maior potencial cariostático que a resina composta com sistema adesivo dentinário.

Dental wear in horses in relation to the microhardness of enamel and dentine

The microhardness of enamel, primary dentine and secondary dentine was determined in the incisor teeth of 39 horses of three different breeds, trotter horses, Belgian draft horses and Arab horses....